1. Field of the Invention
This invention relates to a method of measuring by a coordinate measuring instrument, and is used for measurement automated by a robot of manually operated type coordinate measuring instrument, in particular.
2. Description of the Prior Art
To measure dimensions, contour and the like of a work to be measured, which has a complicated contour, in general, coordinate measuring instruments have been widely used.
The following two types of coordinate measuring instruments are known. Namely, one of those is a manual type, wherein an operator grasps a probe or a portion close to the probe, successively brings the probe into abutting contact with a measuring surface of the work in accordance with predetermined measuring steps, and the dimensions, contour and the like of the work are sought from a displacement value of the probe at the time of contact. The other is an automatic type, for example, a CNC (Computer Numerical Control) tri-dimensional measuring instrument, wherein a main body of measuring instrument is provided thereon with driving means such as a screw and motor for moving the probe in respective directions, of X-, Y- and Z-axes, and the probe is successively brought into abutting contact with the measuring surface of the work while these driving means are automatically controlled in accordance with previously programmed steps.
The former type is simplified in construction, whereby there are few factors affecting the measuring accuracy due to the construction, so that a measured value with high accuracy can be advantageously obtained. On the contrary, the following disadvantages are presented. Namely,
(1) Since the operator must remember all of the portions to be measured and all of the steps with every work, a mistaken operation tends to occur. Moreover, this situation changes with every work.
(2) Simultaneously with the above, operations associated with a data processing unit are needed, whereby specialized and technical knowledge is required from the operator. In consequence, it cannot be said everybody can perform the operations. As viewed from the mode of measuring, the specialist is occupied by the measuring instrument and cannot be utilized for any other operation. Furthermore, it is difficult to gather many such specialists.
(3) With a large-sized measuring instrument permitting a large measuring scope, when all of the measuring points of the work are measured, the measurer should move around the measuring instrument or operate the measuring instrument from a measuring stand, whereby the measuring efficiency is lowered and the safety lacks.
(4) When the operating time period is extended, the temperature of body is imparted from hand to the probe and the like, with the result that the measuring accuracy may be lowered due to the thermal expansion of the probe and the like.
In contrast thereto, the latter type has obviated the disadvantages in the former and is suitable for the repeated measurements of works, which are identical with one another. On the contrary, in order to automatically move the probe in the directions of X-, Y- and Z-axes, driving means such as a screw, motor and the like should be mounted to a main body of the measuring instrument, particularly to a slider supporting a probe shaft, and further, to a beam supporting the slider, whereby the construction for supporting the above-described members cannot but be large-sized. Then, distortions, and deflections are caused to the structure of the foundation with the increase in the weight of the above-described members, with the result that the measuring accuracy is disadvantageously lowered.